EP1065684B1 - Electrical switching device having a contact with a spark protection device - Google Patents

Abstract

Electric switch has contact bridge (24) with housing (70) used for supporting two contact blades (56, 58). One blade has lateral zone for arc transfer situated to larger distance relative to median plane than contact zone of blade. Switch also includes spark suppressor (40) linked to fixed blade (20, 22). When contact bridge is in its opened position, shortest distance between spark suppressor and contact bridge is measured between zone for arc transfer and corresponding zone on lateral parts of suppressor, and this distance is smaller than shortest distance between contact bridge and fixed blade.

Description

The invention relates to an electrical switchgear, in particular an electrical switch, comprising a fixed knife contact member and a movable contact member.

US-A-4,778,961 discloses an electrical switchgear according to the preamble of claim 1.

Conventional apparatus of this type is shown for purposes of illustration in Figure 1 in the closed position, and in Figure 2 in the open position. A pole 110 of this apparatus comprises a fixed contact member in the form of a knife 112, a movable contact member 114 pivoting and a breaking chamber 116 with separators 118. The movable contact member 114 comprises two parallel blades, of which only one is visible in the figures, and which together form a clamp. The two members 112, 114 are elongate and placed more or less in the extension of one another so that in the closed position, the two blades of the movable contact member pinch the two side faces of the knife. FIGS. 1 and 2 show the locations A and B of the corresponding respective contact points on the knife and on the blades of the movable contact. Current lines 120 flowing between the two connection areas are substantially loopless. Upon opening, the movement of the contact zone of the movable contact member follows a direction substantially perpendicular to the direction that the current lines had before opening, so that the electric arc 122 which is born between the contact areas at the last points of contact A, B tends to leak towards the ends of the two contact members at A 'and B'. In particular, the foot of the arc points to A 'in a direction opposite to the breaking chamber 116. This displacement is not favorable to an entrance of the arc into the chamber. In conventional equipment, the ionization generated by the arc at the beginning of opening is sufficient for a new arc breakdown to take place along a line of smaller distance between the two contacts, between A "and B '. The geometry of the pole is such that this line is located near the chamber, so that the new arc extends into it, while the first arc goes out.

This mode of operation is satisfactory when the expected performances are low, with overload currents lower, for example, than 6 I _n , where _n is the nominal current. It is no longer suitable when the required performances are higher, for example with overload currents reaching 8 I _n , or when overloading and closing cycles are required. Indeed, the cut-off time with such a device is long, and the stagnation of the arc at the end of the contact members causes excessive erosion of the contact areas when the overload currents are large.

In order to limit the movement of the foot of the electric arc towards the end of the fixed contact member without increasing the size of the apparatus, the French patent application bearing the deposit number 9816783 teaches that advantage that the fixed contact member has a slot disposed between its contact zone and its connection zone, close to its contact zone, and opening on the side of the first contact member facing the contact zone of the second contact member in the open position. When the contact members are in the closed position, the current lines propagate in the material of the first contact member approximately in its longitudinal direction. When opening, the effective contact surfaces between the two contact members tend to move in the direction of opening, and the current lines are forced to bypass the slot and follow a direction approximately parallel to the sidewall the slot located on the side of the contact area. At the time of separation of the contact members, the current lines curved in the first contact member are relatively stable, so that the foot of the arc has little tendency to leak towards the free end of the contact member. . Due to the movement of the head of the arc towards the end of the second contact member, which is carried out in the same manner as in the state of the art described above, the arc moves away generally from the free end of the first contact member.

This provision is effective, but insufficient for some devices, including small caliber. The emission of gas from the walls of the polar compartment is then indeed insufficient to allow reclamation of the arc at the entrance of the chamber. In addition, the market imposes for such devices a very small footprint, so a small distance between the contacts in the open position. For these reasons, the electric arc tends not to extend into the arc extinguishing chamber. The stagnation of the arc on the moving contact causes erosion of the contact and the formation of metal balls which subsequently hinder the reclosing.

The invention aims to eliminate the disadvantages encountered with the state of the art, and in particular to eliminate the risk of formation of metal balls on the movable contact member, without increasing the size of the switch.

According to the invention, this problem is solved by means of an electrical switchgear, in particular an electrical switch, comprising at least: a fixed contact member with an elongate knife defining a longitudinal median plane and a contact zone; a movable clamping contact member comprising at least two contact blades facing each other on either side of the median plane and each moving in a plane parallel to the median plane, each of the blades comprising a contact zone, the organ mobile contact being able to take a closed position in which the two blades pinch the knife of the fixed contact member, the contact areas of the blades then being in contact with the contact zone of the knife, and an open position in which two blades are remote from the fixed contact member, apparatus in which at least one of the blades of the movable contact member comprises a lateral zone of transfer of the arc, located at a greater distance from the plane median than the contact zone of said blade; the apparatus further comprising a metal spark arrester secured to and in electrical contact with the fixed contact member, the spark arrester having a curved upper flange with a medial portion located a short distance from the fixed contact member and at least one lateral portion located at a greater distance from the median plane and the fixed contact, the spark arrester being shaped and arranged in such a way that when the movable contact member is in its open position, the shortest distance between the spark gap and the movable contact member is measured between the arc transfer zone and a corresponding zone of said lateral portion of the upper edge of the plate, and that this distance is smaller than the shortest distance between the movable contact member in the open position and the fixed contact member. Thus, the head of the electric arc, even if it is born near the contact areas of the movable contact member, migrates rapidly to the lateral transfer zone, so that if a metal ball is formed, it is at this side area, at a place where it can not interfere with the reclosing of the device.

Preferably, the device is symmetrical: the upper edge of the spark gap is approximately U-shaped or V shaped, with a median portion located at a short distance from the fixed contact member and two side portions substantially symmetrical to each other relative to the median plane, located at a greater distance from the median plane and the fixed contact. Each of the two blades of the movable contact member comprises a lateral zone of transfer of the arc, located at a greater distance from the median plane than the zone of said blade coming into contact with the fixed contact member. closing position, the two lateral zones of stagnation of the arc being approximately symmetrical with respect to each other on each side of the median plane, so that the shortest distance between the spark-gap and the movable contact is measured between one or the other of the arc transfer zones and a corresponding zone of said corresponding lateral part of the upper edge of the plate, and that this distance is smaller than the shortest distance between the movable contact member in the open position and the fixed contact member.

Advantageously, the spark arrester is made of ferromagnetic material. Indeed, the classical electromagnetic interactions that we encounter in an electric current and a ferromagnetic material are applicable to an electric arc, which is by nature a current.

According to one embodiment, the spark arrester forms a plate.

Preferably, the fixed contact member has two longitudinal ends, the contact area being on the side of one of the longitudinal ends and an electrical connection area being located on the side of the other longitudinal end. The spark arrester is fixed to the fixed contact member in a region of the fixed contact member intermediate between the contact zone and the connection zone. Thus, as soon as the current is diverted into the spark arrester, it definitively leaves the contact zone. With this configuration, it is particularly advantageous to provide that the fixed contact member has a transverse slot located between the contact zone and the connection zone, and that a lower portion of the spark gap is inserted into said slot. The slot has little influence in the closed position, but as soon as the apparatus opens and the current lines are curved in the fixed contact member, it allows to extend the electrical path of the connecting zone to the contact zone by promoting the inflection of the current lines in the material of the fixed contact member in a direction parallel to the slot. In doing so, it promotes the penetration of power lines in the spark arrester, despite the electrical resistance inevitable contact between it and the knife.

In devices of small calibres, the spark screen arranged in the room makes it possible to dispense with the usual separators.

According to one embodiment, the apparatus comprises a second fixed contact member with an elongate knife defining a longitudinal median plane coincident with that of the first fixed contact member, the movable contact member forming a bridge between the two fixed contact members. .

• la figure 1, déjà commentée, représente une vue du mécanisme de l'état de la technique en position fermée ;
• la figure 2, déjà commentée, représente une vue du mécanisme de l'état de la technique en position ouverte ;
• la figure 3 représente une vue en perspective d'un interrupteur tripolaire selon l'invention ;
• la figure 4 représente une vue d'un pôle de l'interrupteur de la figure 3, en position fermée ;
• la figure 5 représente une vue du pôle de la figure 3, en position ouverte ;
• la figure 6 représente une vue en coupe selon la ligne VI-VI de la figure 4 ;
• la figure 7 représente une vue en coupe selon la ligne VII-VII de la figure 5 ;
• la figure 8 représente une vue en éclaté d'un couteau de contact fixe et d'un pare étincelle selon l'invention.

Other advantages and features of the invention will emerge from the following description of an embodiment of the invention, given by way of non-limiting example and shown in the accompanying drawings, in which:

• Figure 1, already commented, shows a view of the mechanism of the state of the art in the closed position;
• Figure 2, already commented, represents a view of the mechanism of the state of the art in the open position;
• FIG. 3 represents a perspective view of a three-pole switch according to the invention;
• Figure 4 shows a view of a pole of the switch of Figure 3, in the closed position;
• Figure 5 shows a view of the pole of Figure 3, in the open position;
• Figure 6 shows a sectional view along the line VI-VI of Figure 4;
• Figure 7 shows a sectional view along the line VII-VII of Figure 5;
• Figure 8 shows an exploded view of a fixed contact knife and a spark arrester according to the invention.

With reference to FIGS. 3 to 8, a switch 10 is housed in a molded insulating casing 12 and comprises three polar compartments 14, 16, 18. Each polar compartment comprises two identical fixed contact blades 20, 22 electrically connected by a contact bridge. mobile 24 rotated about a transverse central geometric axis 26 fixed relative to the housing 12. The knives 20, 22 define a median longitudinal geometric plane 28 visible in Figures 6 and 7, perpendicular to the axis of rotation 26. In a known per se, the contact bridges 24 of the different compartments are connected to a common control device so that all the bridges are simultaneously in the same angular position relative to the corresponding knives. However, in order not to unnecessarily increase the number of figures, FIG. 3 shows the bridges of the compartments 16 and 18 in the closed position corresponding to FIGS. 4 and 6 while the deck of the compartment 14 is shown in the open position. , corresponding to Figures 5 and 7.

The knife 20, 22 of each fixed contact member, visible in FIG. 8, has on the side of one of its longitudinal ends a beveled portion 30 forming an access ramp to a contact zone 32 and intended to cooperate with the contact bridge and, on the opposite side, a connection pad 34 for connection to the network. A transverse slot 36 partially separates the contact zone 32 from the connection zone 34. A spark screen 40 is fixed at this slot. The spark arrester 40 is constituted by a plate 42 with a lower rim 44 comprising an attachment zone provided with notches 46 intended for fixing in the slot, and an upper rim 48 curved approximately in U or V, with a median portion 50 and two side portions 52, 54. The spark gap plate is symmetrical with respect to its plane and with respect to a second plane transverse to the previous one.

When the spark arrester 40 is mounted on the knife 20, 22, it is arranged transversely to a median longitudinal plane of the knife. The symmetries of the plate 42 allow to mount it on the knife 20, 22 indifferently in two directions. The median portion 50 of the upper rim 48 is in continuity with the upper edge 55 of the knife located near the slot, on the side of the slot opposite the contact zone 32.

Each contact bridge 24 comprises a cage 70 serving to support two contact blades 56, 58 held in a median position by not shown elastic means. The two blades 56, 58 of each contact bridge 24 are identical and symmetrical to one another with respect to the median longitudinal plane defined by the knife. Each blade 56, 58 of the contact bridge has, at each of its ends, a boss 60, 62 facing the other blade and, on the opposite face, an arc transfer zone 64, 66.

In the closed position, in Figures 4 and 6, the bosses 60, 62 of the blades 56, 58 of the movable contact bridge are in contact with the contact zone 32 of the corresponding knife 20, 22. The current can then flow between the two knives 20, 22 of each pole, through the bridge 24, the current being shared between the two blades 56, 58 of the bridge.

The construction and arrangement of the contact members of the pole is therefore generally symmetrical with respect to the axis 26.

When the contact bridge 24 pivots about its axis from the closed position to the open position, the bosses 60, 62 slide along the beveled edges of the knife until separation. The tangent to the path of the point of contact on the bosses 60, 62 at the time of separation is substantially parallel to the transverse plane of the plate 42 forming the spark gap 40, or made with it a small angle. When the bridge continues to pivot, the distance between the bosses 60, 62 of the deck blades and the corresponding knife 20, 22 grows faster than the distance between the lateral edge of each of the transfer zones 64, 66 and the upper edge 48 of the spark screen. After a few additional degrees of rotation, the smallest distance between the contact bridge and the assembly consisting of the knife and the spark arrester is measured between the outer lateral edge of the transfer zones 64, 66 and a corresponding point of the lateral portion 52, 54 of the upper flange 48 of the spark gap 40. In practice, the smallest distance is then a few millimeters, typically 2 millimeters. When the bridge 24 continues its rotation to its open position shown in Figures 5 and 7, this point follows a path on the edge of the rim of the spark arrester, trajectory that gradually deviates from the median longitudinal plane of the knife .

Due to the symmetry of the device with respect to the axis 26, the foregoing description of the opening movement is valid for both the knife 20 and the knife 22.

The operation of the device is then as follows. If an electric arc arises between one of the bosses 60, 62 of the contact bridge and the knife 20, 22 at the time of the separation of the contacts, the current lines in the knife material tend to bend to circumvent the slot 36 in which is engaged the spark arrester, so that the foot of the arc is close to the spark arrester. This effect is accentuated by the magnetic mass constituted by the spark screen. Gradually, the distance between the blades 56 and 58 of the contact bridge and the spark arrester 40 becomes smaller than the distance between the blades 56, 58 and the knife 20, due to the rotation of the bridge. Quickly, the arc migrates or recalls between the spark arrester 40 and one or other of the blades 56, 58, due to the lower dielectric strength in this region of the chamber. Because of the symmetries of the device, the choice of one or the other blades is relatively random, depending on the initial conditions. Certain involuntary dissymmetries of realization can also influence the phenomenon. The power lines then enter the spark arrester 40 via the contact interface between the spark arrester 40 and the knife 20.

When the contact bridge 24 continues its rotation, the arc tends to move so as to minimize its energy at all times. Since the minimum energy is approximately constant at each instant for an arc along a line of shorter distance between the spark arrester and the bridge, the foot of the arc moves along the rim 48 of the spark arrester laterally away from each other. the median longitudinal plane 28 of the knife and the median portion 50 of the rim. Depending on the initial conditions, the arc chooses one of the two lateral sides. This movement of the foot of the bow naturally promotes a movement of the head of the arc laterally towards the face 64, 66 farthest from the median longitudinal plane 28 of the conductor 56, 58 placed on the corresponding side. The head of the arc does not remain permanently at the bosses 60, 62, which prevents the melting of the metal at this location. If a fusion takes place, it is at the place where the arc is parked at the end of the opening, that is to say on the lateral lateral side 64 or 66 of one of the blades of the bridge. The drop of metal possibly formed does not interfere at this point with the subsequent closure of the apparatus.

Naturally, various variations are possible without departing from the scope of the invention. The embodiment shown relates to a rotary switch, but the invention is also applicable to a switch whose moving contact moves in translation, of the type illustrated for example in EP-A-0 100 699.

Furthermore, the invention is also applicable to switches comprising a movable contact member connected directly to a connection pad in place of the bridging contact connecting two fixed contacts.

We can also do without the slot if the target performance for the switch is not too high. Similarly, the constitution of the spark gap plate of ferromagnetic material is optional.

The shape of the spark screen is not necessarily flat.

The symmetries of the embodiment described above has a practical advantage in the assembly of the equipment, since many parts are identical (the two blades of the bridge, the two knives, the two pares sparks, etc ...), and that the constraints on the assembly direction of the parts are reduced.

However, it is possible to deliberately choose a form of asymmetric spark guard, or to define blades 56, 58 different from each other, especially in order to promote movement towards one of the lateral sides of the chamber rather than towards the other.

Claims (8)

1. Electrical switchgear apparatus, in particular an electrical switch, comprising at least:

   - a stationary contact means (20, 22) in the form of a long slender blade defining a longitudinal mid-plane (28) and a contact zone (32);

   - a movable contact means (24) in the form of a grip comprising at least two contact fingers (56, 58) facing one another on each side of the mid-plane (28) and both moving in a plane parallel to the mid-plane, each of the fingers comprising a contact zone (60, 62), the movable contact means being able to take a closed position wherein the two fingers (56, 58) grip the blade (20, 22) of the stationary contact means, the contact zones (60, 62) of the fingers (56, 58) then being in contact with the contact zone (32) of the blade, and an open position wherein the two fingers (56, 58) are separated from the stationary contact means (20, 22),

   characterized in that:

   - at least one of the fingers (56, 58) of the movable contact means comprises a lateral arc transfer zone (64, 66) situated at a greater distance with respect to the mid-plane (28) than the contact zone (60, 62) of said finger;

   - the apparatus comprises in addition a metallic spark arrester (40) securedly united to the stationary contact means (20, 22) and in electrical contact with the latter, the spark arrester (40) having a curved top edge (48) with a middle part (50) situated at a small distance from the stationary contact means (20, 22) and at least one lateral part (52, 54) situated at a greater distance from the mid-plane and from the stationary contact, the spark arrester being shaped and arranged in such a way that when the movable contact means (24) is in its open position, the shortest distance between the spark arrester (40) and the movable contact means (24) is measured between the arc transfer zone (64, 66) and a corresponding zone of said lateral part (52, 54) of the top edge of the plate, and that this distance is smaller than the shortest distance between the movable contact means (24) in the open position and the stationary contact means (20, 22).
2. Electrical switchgear apparatus according to claim 1, characterized in that:

   - the top edge (48) of the spark arrester is approximately U-shaped or V-shaped, with a middle part (50) situated a small distance from the stationary contact means (20, 22) and two lateral parts (52, 54) appreciably symmetrical to one another with respect to the mid-plane (28), situated at a greater distance from the mid-plane (28) and from the stationary contact (20, 22),

   - both of the fingers (56, 58) of the movable contact means comprise a lateral arc transfer zone (64, 66) situated at a greater distance with respect to the mid-plane than the zone of said finger coming into contact with the stationary contact means in the closed position, the two lateral arc stagnation zones being approximately symmetrical to one another on each side of the mid-plane,

   so that the shortest distance between the spark arrester (40) and the movable contact means is measured between one or the other of the arc transfer zones (64, 66) and a corresponding zone of said corresponding lateral part (52, 54) of the top edge of the plate, and that this distance is smaller than the shortest distance between the movable contact means in the open position and the stationary contact means.
3. Electrical switchgear apparatus according to either one of the claims 1 or 2, characterized in that the spark arrester (40) is made of ferromagnetic material.
4. Electrical switchgear apparatus according to any one of the above claims, characterized in that the spark arrester (40) forms a plate.
5. Electrical switchgear apparatus according to any one of the above claims, characterized in that the stationary contact means comprises two longitudinal ends, the contact zone (32) being located on the side where one of the longitudinal ends is located and an electrical connection zone (34) being situated on the side where the other longitudinal end is located, and that the spark arrester (40) is fixed to the stationary contact means in a zone of the stationary contact means intermediate between the contact zone and the connection zone.
6. Electrical switchgear apparatus according to claim 5, characterized in that the stationary contact means comprises a transverse slot (36) situated between the contact zone (32) and the connection zone (34), and that a bottom part (46) of the spark arrester is inserted in said slot.
7. Electrical switchgear apparatus according to any one of the above claims, characterized in that it comprises an arc extinguishing chamber wherein the spark arrester extends and which does not comprise separators.
8. Electrical switchgear apparatus according any one of the above claims, characterized in that:

   - the apparatus comprises a second stationary contact means (20, 22) with a long slender blade defining a longitudinal mid-plane which is the same as that of the first stationary contact means,

   - the movable contact means (24) forms a bridge between the two stationary contact means.

Images